1.1 The purpose of this guide is to establish a framework and context for process understanding for pharmaceutical manufacturing using quality by design (QbD) (Juran, 1992; FDA/ICH Q8). The framework is applicable to both active pharmaceutical ingredient (API) and to drug product (DP) manufacturing. High (detailed) level process understanding can be used to facilitate production of product which consistently meets required specifications. It can also play a key role in continuous process improvement efforts.

1.2 Process Analytical Technology (PAT) is one element that can be used for achieving control over those inputs determined to be critical to a process. It is important for the reader to recognize that PAT is defined as: